A lattice of large metal I-beams holds the hollow casings in place while they’re vibrated into the muck of the river bottom and then into the rock beneath that. Eventually, the muck and rock will be removed and concrete poured into the cylinders.

The design is similar to the one Johnson Brothers used when it built the stretch of the Riverwalk beneath the Brorein Street bridge, though larger in scale, said project manager John Meagher.

The pilings going in off Curtis Hixon and Rivergate Tower trace the outline of the first two curving segments of the plaza. The next set of pilings will go under the Kennedy Boulevard Bridge sometime next week, Meagher said.

The $8.8 million Riverwalk segment will close the gap between Curtis Hixon and MacDill Park by running just above the surface of the Hillsborough River. The project should be finished by November 2014.

Unlike other Riverwalk segments, the plaza will include four seating areas for pedestrians and cyclists using the 2.4-mile path.

A U.S. Department of Transportation grant is paying for construction of the plaza and for planning a segment running from Curtis Hixon to the city’s Water Works Park now being redeveloped north of Interstate 275.

The developers of the Residence at the Riverwalk have included the Riverwalk in their own plans. That leg will go overland from across Cass Street and the CSX Railroad tracks because the CSX bridge is too low to build under it.

Last fall, the city secured a 25-year lease of air rights beneath the Kennedy bridge, which is owned by the state Department of Transportation.

The Riverwalk segment will have about 10 feet of clearance between its deck and the underside of the bridge, according to plans.

Riverwalk will fill the underside of the span’s eastern segment, leaving the center and west segments for marine traffic.

The Tampa City Council approved work on the Kennedy Boulevard Plaza in April. At the time, City Councilman Harry Cohen described the project as “one of the most consequential things the city has done for generations.”

This week, Cohen said the finished Riverwalk will be a game changer.

“I think it will invigorate and transform downtown in a way no single project in recent memory has,” he said. “The lack of continuity has always been the biggest impediment to enjoying it.”